A new metabolite of testolactone was isolated from human urine of men taking 2.0 g of testolactone per day. This compound was identified by modern spectroscopic methods and chemical derivatization as D-homo-17Alpha-oxaandrost-1-ene-3,17-dione. Since the concentrations of this metabolite in human plasma are similar to those of the parent compound, the reduced testolactone metabolite may affect assays of the apretn drug. Whether the metabolite contributes to or modifies the pharmacological action of testolactone is unknown.